Campante, T. L.T. L.CampanteBarclay, T.T.BarclaySwift, J. J.J. J.SwiftHuber, D.D.HuberAdibekyan, V. Zh.V. Zh.AdibekyanCochran, W.W.CochranBurke, C. J.C. J.BurkeIsaacson, H.H.IsaacsonQuintana, E. V.E. V.QuintanaDavies, G. R.G. R.DaviesSilva Aguirre, V.V.Silva AguirreRagozzine, D.D.RagozzineRiddle, R.R.RiddleBaranec, C.C.BaranecBasu, S.S.BasuChaplin, W. J.W. J.ChaplinChristensen-Dalsgaard, J.J.Christensen-DalsgaardMetcalfe, T. S.T. S.MetcalfeBedding, T. R.T. R.BeddingHandberg, R.R.HandbergStello, D.D.StelloBrewer, J. M.J. M.BrewerHekker, S.S.HekkerKaroff, C.C.KaroffKolbl, R.R.KolblLaw, N. M.N. M.LawLundkvist, M.M.LundkvistMiglio, A.A.MiglioRowe, J. F.J. F.RoweSantos, N. C.N. C.SantosVan Laerhoven, C.C.Van LaerhovenArentoft, T.T.ArentoftElsworth, Y. P.Y. P.ElsworthFischer, D. A.D. A.FischerKawaler, S. D.S. D.KawalerKjeldsen, H.H.KjeldsenLund, M. N.M. N.LundMarcy, G. W.G. W.MarcySousa, S. G.S. G.SousaSOZZETTI, AlessandroAlessandroSOZZETTIWhite, T. R.T. R.White2020-04-042020-04-04201597815108133422101-6275http://hdl.handle.net/20.500.12386/23837The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2 ± 1.0 Gyr for the host star, indicating that KOI-3158 formed when the Universe was less than 20 % of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, providing scope for the existence of ancient life in the Galaxy.ELETTRONICOenConference paper10.1051/epjconf/2015101020042-s2.0-84960145512000372491300020https://www.epj-conferences.org/articles/epjconf/abs/2015/20/epjconf_sphr2014_02004/epjconf_sphr2014_02004.html2015EPJWC.10102004CFIS/05 - ASTRONOMIA E ASTROFISICAScienze Fisiche Settori ERC (ERC) di riferimento::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation